Carbon capture, utilization and storage (or carbon capture, utilization and sequestration, “CCUS”), is the process of capturing carbon dioxide (CO2) from large point sources, such as fossil fuel power plants, transporting it to a storage and/or utilization site, and depositing/utilizing it where it will not enter the atmosphere. CCUS often involves the storage of the captured CO2 in an underground geological formation such as saline formations, unmineable coalbeds, oil and gas reservoirs, etc. It also includes the utilization of the captured CO2, for example as a pumping fluid for enhanced oil and/or gas recovery from oil and gas reservoirs, as a raw material for producing chemicals and fuels, and for methane recovery from coalbeds. CCUS that does not involve CO2 utilization is often referred to as carbon capture and storage (or carbon capture and sequestration, “CCS”).
Carbon capture is intended to prevent the release of large quantities of CO2 into the atmosphere (from fossil fuel use in power generation and other industries). It is a potential means of mitigating the contribution of fossil fuel emissions to global warming and ocean acidification.
Although CO2 has been injected into geological formations for several decades for various purposes, including enhanced oil recovery, the long term storage of CO2 is a relatively new concept. Today, there exists a growing need for developing new methods of capturing, storing, and transporting captured carbon dioxide.
CCUS applied to a modern conventional power plant could reduce CO2 emissions to the atmosphere by approximately 80-90% compared to a plant without CCUS. The IPCC estimates that the economic potential of CCUS could be between 10% and 55% of the total carbon mitigation effort until year 2100.
Capturing CO2 is probably most effective at point sources, such as large fossil fuel or biomass energy facilities, industries with major CO2 emissions, natural gas processing, synthetic fuel plants, cement plants, iron and steel plants, ethanol plants, and fossil fuel-based hydrogen production plants. Extraction (recovery) from air is possible, but not very practical. The CO2 concentration drops rapidly moving away from the point source. The lower concentration increases the amount of mass flow that must be processed (per ton of carbon dioxide extracted).
Concentrated CO2 from the combustion of coal (e.g., at power plants) in oxygen is relatively pure, and could be directly processed. Impurities in CO2 streams could have a significant effect on their phase behavior and could pose a significant threat of increased corrosion of pipeline and well materials. In instances where CO2 impurities exist and especially with air capture, a scrubbing process would be needed.
In post-combustion capture, the CO2 is removed after combustion of the fossil fuel; Carbon dioxide is captured from flue gases at power stations or other large point sources. Post-combustion capture refers to the removal of CO2 from power station flue gas prior to its compression, transportation and storage in suitable geological formations, as part of carbon capture and storage.
A number of different techniques are applicable, almost all of which are adaptations of acid gas removal processes used in the chemical and petrochemical industries. Many of these techniques existed before World War II and, consequently, post combustion capture is the most developed of the various carbon-capture methodologies.
The acid gas removal process (aka, mine gas treating or gas sweetening) refers to a group of processes that use aqueous solutions of various alkylamines (commonly referred to simply as amines) to remove hydrogen sulfide (H2S) and carbon dioxide (CO2) from gases. It is a common unit process used in refineries, and is also used in petrochemical plants, natural gas processing plants and other industries.
Today, the field of carbon capture needs better molecular separation processes. In particular, the field would benefits from new methods of capturing carbon dioxide that do not require the traditional acid gas removal process.
There also exists a need for limiting methane losses and purifying methane that is contaminated with carbon dioxide. The ongoing need for purifying methane is especially important in circumstances having a wide range of feed compositions, such as feeds with multiple CO2 compositions ranging from CO2-lean to CO2-rich methane sources.
In pursuit of better carbon dioxide capture and methane purification, the art would benefit from developing better adsorbents (e.g., zeolites and MOFs) for pressure swing adsorption (PSA) and vacuum swing adsorption (VSA) processes. Similarly, carbon capture and methane purification technology has an ongoing need for better PSA and VSA methods, which offer more cost efficient ways of separating carbon dioxide from molecular mixtures comprising carbon dioxide.
Improvements in PSA and VSA methods would have far reaching benefits, including Natural gas purification, bio-syngas purification, bio-fuel purification, xylenes purification, hydrogen purification, propane/propylene separation, ethane/ethylene separation, and other gaseous separations of molecules.